In harvesting a crop with a combine, it is desirable to adjust the ground speed so as to feed the crop to the processor at a rate that permits it to be efficiently threshed and cleaned without excessive loss of grain in discharged material. Heretofore, various automatic ground speed controls have been proposed to match the intake of crop to the threshing and cleaning capability of the combine. In some such automatic controls, the ground speed is controlled by an apparatus which senses the work load or torque requirements of one or more power consuming operations of the combine. In others, the ground speed control is responsive to an apparatus which senses grain loss. When operating a combine with an automatic ground speed control, conditions may arise which require a quick change to manual ground speed control. Some such conditions which might arise would include the sudden appearance of a gully, obstacle or livestock ahead of the combine. Thus, it is normal for such prior art automatic ground speed controls to have some means for allowing the operator to change to manual control of combine speed.